1. Field of the Invention
The present invention relates to an image switching apparatus, and in particular to an image switching apparatus that provides an optical compensator.
2. Description of the Related Art
A digital camera is usually provided with a preview function.
Referring to FIG. 1, a conventional camera 1 includes a lens 11, a fixed beam splitter 12 and an image sensor 13. The lens 11 is composed of multiple lenses. An included angle of 45° exists between the fixed beam splitter 12 and the image sensor 13. The image sensor 13 may be a CCD. As shown in FIG. 1, when the camera 1 receives an input image S1 projected from the lens 11, the input image S1 is also projected on the image sensor 13 and a viewfinder 14 via the fixed beam splitter 12. Namely, the input image S1 is divided into two parts by the fixed beam splitter 12. One part of the input image S1 penetrates the fixed beam splitter 12 and is incident on the image sensor 13 while the other part of the input image S1 is reflected upward by the fixed beam splitter 12 and projected on the viewfinder 14. Accordingly, a user can simultaneously preview and capture the input image S1.
The camera 1, however, has a drawback as follows. Since the input image S1 is divided into two parts by the fixed beam splitter 12, light intensity of the input image S1 projected on and received by the image sensor 13 is reduced, adversely affecting imaging thereof. Specifically, the aforementioned problem becomes worse when environmental light intensity is insufficient.
Referring to FIG. 2, another conventional camera 2 can overcome the drawback of the camera 1. The major difference between the two cameras 2 and 1 is that the camera 2 employs a rotatable beam splitter 12′ to replace the fixed beam splitter 12. As shown in FIG. 2, when the rotatable beam splitter 12′ rotates toward the image sensor 13 with an included angle of 45° (as shown by dotted portion), an input image S2 projected from the lens 11 is divided into two parts by the rotatable beam splitter 12′. One part of the input image S2 is reflected by the rotatable beam splitter 12′ and projected on the viewfinder 14. At this point, the user can preview the input image S2. In another aspect, when the user wants to capture the input image S2, the rotatable beam splitter 12′ can be rotated clockwise to the upper portion of the lens 11. At this point, the image sensor 13 can receive the input image S2 with enhanced light intensity without obstruction of the rotatable beam splitter 12′.
Accordingly, in the absence of the rotatable beam splitter 12′ between the image sensor 13 and the lens 11, the lens 11 forms an image plane behind the image sensor 13. Namely, the input image S2 received by the image sensor 13 is thus blur.